Download Production and detoxification mechanisms of methylglyoxal in

P010
Production and detoxification mechanisms of methylglyoxal
in photosynthetic organisms: photosynthesis stimulated the
production of methylglyoxal
Ginga Shimakawa1 and Chikahiro Miyake2
1
Kobe University, Kobe, Japan
2
Graduate School of Agricultural Science, Kobe University,
Kobe, Japan
Methylglyoxal (MG) is produced in the equilibration reaction
between dihydroxyacetone phosphate (DHAP) and glyceraldehydes
3-phosphate (GAP) catalyzed by triose phosphate isomerase (TPI)
in the glycolysis. TPI also functions in the Calvin cycle of photosynthetic organisms. We tried to detect MG during photosynthesis
in intact chloroplasts isolated from plants leaves. Orthophenylene
diamine-derived MG was analyzed by HPLC-system. In the Calvin
cycle of chloroplasts, 3-phosphoglycerate (3-PGA) is metabolized
to GAP catalyzed by PGA kinase and GAP dehydrogenase sequentially, and GAP was equilibrated with DHAP. The addition of 3-PGA
to the illuminated chloroplasts induced photosynthetic O2 evolution
and MG production. The production rate of MG increased with the
increases in light intensity and 3-PGA concentration. These results
indicated that the production of MG is inevitable in the photosynthesis and the stimulation of photosynthesis enhances the MG toxicity.
We furthermore sought glyoxalase system in the origin of oxygenic
photosynthetic organisms, cyanobacteria. Cyanobacteria are the
prokaryotes, that is, photosynthesis and respiration occur in the same
compartment of the cytosol. Therefore, cyanobacteria are exposed
to the much stronger sugar-toxicity, compared to higher plants. We
found the gene, SyGLX1 in Synechocystis sp. PCC6803 (S. 6803),
homologous to AtGLX1 (At1g11840) in Arabidopsis thaliana and
SyGLX2, homologous to AtGLX2 (At3g10850). Both GLX1 and
GLX2 showed the activities of glyoxlase systems. We wild report the
detailed analysis of the detoxification mechanisms of sugar-derived
RCs in cyanobacteria.